HR: 09:00h
AN: S31B-05    [Abstracts]
TI: Sintered cataclasite of the Archaean Pretorius fault zone, TauTona mine, South Africa
AU: * Zechmeister, M S
EM: zechmeim@ou.edu
AF: School of Geology and Geophysics,The University of Oklahoma, 100 E. Boyd St., Norman, OK 73019 United States
AU: Heesakkers, V
EM: Vincent.Heesakkers-1@ou.edu
AF: School of Geology and Geophysics,The University of Oklahoma, 100 E. Boyd St., Norman, OK 73019 United States
AU: Moore, K
EM: kate_moore@ou.edu
AF: School of Geology and Geophysics,The University of Oklahoma, 100 E. Boyd St., Norman, OK 73019 United States
AU: Campher, C
EM: 2219851@uwc.ac.za
AF: Earth Science Department, The University of Western Cape, Private Bag X17, Bellville, 7535 South Africa
AU: Reches, Z
EM: reches@ou.edu
AF: School of Geology and Geophysics,The University of Oklahoma, 100 E. Boyd St., Norman, OK 73019 United States
AB: We have studied the exposures of the Pretorius fault at depth of ~ 3.5 km in the TauTona gold mine, South Africa, as part of the NELSAM project (earthquakes.ou.edu). The Pretorius fault has been inactive since the Archaean and is a 10 km long fault with 30-60 m of throw and suspected horizontal slip of ~ 200 m (Heesakkers et al, this meeting). Its fault-zone is ~25 m wide with tens of cross-cutting segments that display one distinct fault-rock which was previously classified as a mylonite or pseudotachylite. We refer to this enigmatic rock as `sintered cataclasite', and we present here its structural and mineralogical characteristics and discuss possible mechanisms for its formation. The sintered cataclasite is a highly cohesive and massive rock that ranges in color from grey to green, which appears in veins along the fault segments. These veins range in thickness from a few millimeters to tens of centimeters, and are locally continuous for tens of meters. The veins vary significantly in thickness with common pinching out along a given host segment. Some of the cataclasite veins carry secondary injection veins that penetrated the host blocks at high angles to the segment surface. The sintered cataclasite is composed of a cohesive, fine-grain quartzitic matrix, with abundant angular to sub-rounded fractured quartz and opaque minerals clasts that are 0.01-0.5 m in size. Flow features can be identified in the sintered cataclasite by the presence of injection veins and wall-parallel flow banding. We did not find evidence for vein-parallel shear, e.g. rotated clasts, or evidence of large-scale melting, e.g. microlites or partially melted clasts (these rocks cannot be regarded as pseudotachylites). SEM image analysis revealed "hour glass" contacts between quartz grains that suggest sintering of a granular material after granulation. Multiple slip events were recognized in a few fault segments by the presence of cleavage with kinked micas and cross-cutting cataclasite veins. We propose that the studied cataclasites formed by post-faulting sintering of non-cohesive gouge zones, which were produced by pulverization of the host quartzite during Archaean earthquakes. This concept is based on the geometric and grain-size similarities between the rock powder that forms during recent rock failure in the mines and the sintered cataclasite. The injection veins indicate fluidization without melting of the pulverized gouge into zones of lower pressure during the seismic events.
DE: 7209 Earthquake dynamics (1242)
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8034 Rheology and friction of fault zones (8163)
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Seismology [S]
MN: Fall Meeting 2005